of Ketonization of the Enol of 4-Phenyl-1-Benzoylcyclohexane. In this example the enol intermediate is generated from either the cis- or the trans-stereoisomer of 1-bromo-1-benzoyl-4-phenylcyclohexane using zinc as the reagent. The endo proton approach is blocked by two axial hydrogens. This example is somewhat more typical than those shown earlier since the stereoselectivity is only in the range of 60 to 70 percent favoring formation of the (less stable) cis product. References Stereochemistry Organic reactions